Farmscape for March 22, 2023

PRRS and porcine circovirus have been shown to disrupt thyroid hormone levels leading to reduced growth performance.
Researchers with the Western College of Veterinary Medicine have been exploring the effect of disease on thyroid hormone levels in pigs and potential treatment options for the reductions in growth performance caused by fluctuating levels.
Dr. John Harding, a professor in the Department of Large Animal Clinical Sciences with the Western College of Veterinary Medicine, explains scientists looked at thyroid hormone levels in sera from salmonella and Mycoplasma hyopneumoniae trials conducted by Iowa State University, from a salmonella study by the Prairie Swine Centre, from a PCV2 trial by the University of Nebraska and from Brachyspira trials and a PRRS-mycoplasma coinfection trial by the WCVM.

Clip-Dr. John Harding-Western College of Veterinary Medicine:
Of those five diseases, we really found solid evidence of a prolonged suppression in thyroid hormone in only the PCV trial and the PRRS-mycoplasma coinfection trial.
Interestingly, with mycoplasma alone and with Brachyspira and salmonella, there was no sustained suppression.
There was nothing that you could say over a large period of time or a long period of time thyroid hormones were suppressed.
So, it's very interesting that this does appear to be an issue specific to PRRS and to circovirus.
So, we know there are at least two viruses, PRRS and circovirus that dysregulate the thyroid metabolism, at least transiently for that two-to-three-week period.
This helps us to understand why growth rates may be slowed when pigs are infected by these.
There is also considerable pig to pig variation in response to PRRS virus so there may be an opportunity to select for more resilient pigs.
That would those that have less suppression following infection and they would grow faster.

Dr. Harding notes certain thyroid hormone levels have been found to have low to moderate heritability so it is possible to select for resilient animals if there is a desire to do that.
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Bruce Cochrane.

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